Wear characteristics of Fe–25Cr–C–B eutectic cast alloys

Abstract

To clarify the characteristics of Fe–25Cr–C–B cast alloys, a pin on disc friction and wear test was conducted on Fe–25Cr–0C–2.2B, Fe–25Cr–2.2C–1.0B and Fe–25Cr–3.5C–0B eutectic alloys, at various sliding velocities ranging from 0.125 to 1.99 m s^-1. The effects of sliding velocity on the wear resistance of these alloys were studied by the pin on disc friction and wear test, SEM and an X-ray diffraction method. The results show that the effects of sliding velocity on the increase in wear loss were different due to the differences in structure among the alloys. The X-ray diffraction method shows the presence of Fe₂ O₃ and Fe₃ O₄ in the alloys after conducting wear tests for almost all of the wear conditions. From the sliding velocity dependence of wear loss, worn surface observation after the wear tests and X-ray diffraction results, the relationships between the type of oxide and wear loss for Fe–25Cr– 0C–2.2B and Fe–25Cr–2.2C–0B alloys are not clear. However, the wear loss of Fe–25Cr–3.5C–0B alloy decreases at a sliding velocity of 0.5 m s^-1 or lower, due to the presence of red Fe₂ O₃ oxide on the worn surface. The wear loss peaks at a sliding velocity of 0.95 m s^-1, and decreases again at a sliding velocity of 1.99 m ^-1 due to the presence of black Fe₃ O₄ oxide.     

Influence of graphite morphology on dry sliding wear of flake graphite cast irons

Abstract

Four flaky graphite cast irons of different graphite structures with a pearlitic matrix were prepared to clarify the graphite structure's influence on the dry sliding wear property. Two melts of cast iron with different carbon contents were solidified at two different cooling rates. The four resultant samples had type A flaky graphite or type D eutectic graphite structure with different graphite volume fractions and fully pearlitic matrixes. A pin on the disc type wear test evaluated the four samples' dry sliding wear properties. Results showed that the type D graphite structure wore down faster than the type A graphite structure did. The type of graphite morphology influenced the specimen wear rate as strongly as the graphite volume fraction did in flaky graphite cast irons of this experimental range.     

Effect of material and test parameters on wear behaviour of eutectic Al–Si alloy (LM13)

Abstract

This paper investigates the effects of contact pressure, sliding speed and alloy condition on dry sliding wear behaviour of LM13 (Al–12Si–0˙8Cu–1˙0Ni–0˙6Mg) alloy. A pin on disc type wear testing machine was used to study the wear behaviour of alloy in untreated, melt and heat treated condition. Dry sliding wear tests were performed at two contact pressures (0˙31 and 0˙93 MPa) and four sliding speeds (0˙2, 0˙5, 0˙9 and 2˙0 m s^–1). The wear rate decreased with the increase in sliding speed irrespective of contact pressure and alloy condition used in this work. The untreated alloy exhibited higher wear rate than melt and heat treated alloy. The refinement of eutectic Si by melt treatment and spheroidisation of eutectic Si after heat treatment of LM13 alloy have been attributed to the reduction in wear. Melt treatment and heat treatment of LM13 alloy increased the hardness and tensile strength, while increase in ductility was marginal.     

Determination of lower bound fracture toughness of a high strength low alloy steel welded joint

Abstract

The use of high strength low alloy steels for high performance structures (e.g. pressure vessels and pipelines) requires high strength consumables to produce an overmatched welded joint. This globally overmatched multipass welded joint contains two significantly different microstructures, as-welded and reheated. In this paper, the influence of weld metal microstructure on fracture behaviour is estimated in comparison with the fracture behaviour of composite microstructures (as-welded and reheated). The lower bound of fracture toughness for different microstructures was evaluated by using the modified Weibull distribution. The results, obtained using specimens with crack front through the thickness, indicated low fracture toughness, caused by strength mismatching interaction along the crack front. In the case of through thickness specimens, at least one local brittle microstructure is incorporated in the process zone at the vicinity of the crack tip. Hence, unstable fracture occurred with small, or without, stable crack propagation. Despite the fact that the differences between the impact toughness of a weld metal and the that of base metal are insignificant, the fracture toughness of a weld metal can be significantly lower.     

Numerical analysis of heat transfer process for double sided tungsten inert gas – metal inert gas weld pool

Abstract

Double sided arc welding is a new type of technology developed in recent years. Many experiments show that this technology has great advantages over single arc welding for the joining of intermediate thickness stainless steel and aluminium alloy base metals. In the present work, a three-dimensional transient numerical model is created to reveal the heat transfer process for a double sided tungsten inert gas (TIG) - metal inert gas (MIG) weld pool from the viewpoint of heat transfer literature and hydrodynamics. Considering of the features of the model, effective calculation software using finite element technology is adopted. The temperature fields in the weld pool for double sided TIG - MIG welding are successfully calculated; in addition, the configuration of the weld pool is also calculated.Comparisons show that thecalculatedresults agree approximately with the experimentally measured results. STWJ/310     

New technological methods and designs of stir head in resistance friction stir welding

Abstract

This paper proposes a new welding method, resistance friction stir welding (RFSW), which provides a novel method to solve some of the challenges of friction stir welding high melting point of ferrous and non-ferrous metals. The RFSW is a new hybrid welding technology, which utilises the advantages of both resistance welding and friction welding. The technological principle of RFSW uses the compound effects of resistance heating and friction heating; the integration methods are discussed and analysed in this paper. It is believed that RFSW is an innovative, practical welding technique. The national patents for invention have already been applied in China.     

Effect of dynamic contact resistances on advanced high strength steels under medium frequency DC spot welding conditions

Abstract

The effect of dynamic contact resistance (DCR) during MFDC spot welding of dual phase and martensitic steels was evaluated. A comparative analysis of DP590 to DP590 with DP780 to DP780 steel welds, and DP780 to DP780 with M1200 to M1200 steels welds was carried out. The DCR of DP780 steel is higher than DP590 steel during the initial stages of weld time, but is reversed later. The bulk resistance component, which is higher in DP780 steel, is dominant and generates more energy early in the process and controls melting. Although the total energy input is almost same, the higher β-peak and its early occurrence ensures better heat utilisation resulting in larger nugget size. Contrarily, in martensitic steel the interface resistance component remains high throughout the entire welding process and compensates for the lower bulk resistance effect. Even with relatively lower energy input the nuggets produced in M1200 steel are comparable to DP780 steel.     

Influence of initial gap on weld expulsion in resistance spot welding of dual phase steel

Abstract

The weld expulsion is prone to occur and severely affects the nugget quality when the initial gap between dual phase (DP) steel sheets exist in resistance spot welding (RSW). To investigate the effect of initial gap on weld expulsion, a finite element model was developed to analyse the weld nugget formation process with different initial gaps for DP steels. An estimation method of expulsion occurrence based on the ratio of the nugget radius R_n and the contact radius R_c between sheets was proposed to get the critical initial gap without expulsion. The simulation and experimental results showed that the weld expulsion would not happen until the gap spacing reaches the critical value. The critical initial gap of DP steel is much smaller than that of low carbon steel. For both DP steel and low carbon steel, the critical initial gap would increase with the thickening of the steel sheet.     

Corrosion Behavior of 12CrMoV Steel in Waste Incineration Environments: Hot Corrosion by Molten Chlorides

The corrosion resistance of a 12CrMoV alloy incontact with a molten mixture of (52-48)mol.%PbCl₂-KCl, similar to that found inwaste incineration plants, has been studied. Thecorrosion kinetics have been analyzed using continuous-currentelectrochemical techniques and electrochemical impedancespectroscopy (EIS). Studies were performed to determinethe influence that temperature and the presence of carbon in the salt have on the corrosion rate.Scanning electron microscopy (SEM) and electron-probemicroanalysis (EPMA) were used as additional analyticaltechniques to analyze the corrosion products in order to elucidate the corrosionmechanism.     

Tensile stress–strain and work hardening behaviour of 316LN austenitic stainless steel

Abstract

The true stress (σ)–true plastic strain (?) data of a type 316LN austenitic stainless steel tested at nominal strain rates in the range 3×10^-5–3×10^-3 s^-1 and temperatures of 300–1123 K were analysed in terms of flow relationships proposed by Hollomon, Ludwik, Swift, Voce, and Ludwigson. The applicability of the particular flow relationship is discussed in terms of ‘complete’ and ‘applicable’ range fits of the experimental σ–? data. At all strain rates, in the case of the complete range fit, the Ludwigson equation followed the stress–strain data most closely at 300 K, while in the temperature range 523–773 K, the flow behaviour was described equally well by both the Ludwigson and Voce equations. In the temperature range 823–1023 K, the Voce equation described the flow behaviour most accurately in the case of the complete range fit of σ–? data at all strain rates. The analysis of σ–? data employing the Ludwigson equation in the applicable range fit covering low and intermediate strains, and the Hollomon equation at high strains provided close simulation of the observed flow behaviour in the temperature range 823–1023 K. At high temperatures of 1073 and 1123 K, the Ludwigson equation reduces to the Hollomon equation. The variations in different flow parameters of the Ludwigson and Voce equations with temperature and strain rate exhibited anomalous behaviour at intermediate temperatures because of dynamic strain aging.